Preheat your oven to 375°F (190°C).

Boil salted water and cook lasagna noodles until al dente, about 8-10 minutes. Drain and rinse under cold water.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Sauté the chopped onion until softened, about 5 minutes.

Add 3 tablespoons of unsalted butter to the skillet, letting it melt. Whisk in 3 tablespoons of flour and cook until golden. Gradually pour in chicken broth and half and half, whisking until thickened, about 5-7 minutes. Stir in spinach and minced garlic, seasoning with salt and pepper, then remove from heat.

In a bowl, combine ricotta cheese, egg, half of the mozzarella, and parsley. Mix until well combined.

In a casserole dish, layer spinach sauce, lasagna noodles, ricotta mixture, shredded chicken, and more spinach sauce. Repeat layers and end with spinach sauce.

Top with remaining mozzarella cheese, cover with foil, and bake for 45 minutes.

Remove the foil and broil for an additional 2-3 minutes until cheese is bubbly and golden brown. Watch closely to avoid burning.

Let the lasagna rest for 10 minutes before slicing. Garnish with extra parsley and serve.